四川盆地二叠系火山岩岩相与储层特征

为了给四川盆地火山岩气藏下一步的勘探部署提供依据,综合利用钻井录井、分析化验、测井及地震等资料,在对该盆地二叠系火山岩分类的基础上,研究了不同类型火山岩的岩性特征、岩相特征与岩相分布、储层特征,并确定了控制火山岩储层发育的主要因素。研究结果表明:①该盆地火山岩可综合划分为火山熔岩、火山碎屑熔岩、火山碎屑岩及沉火山碎屑岩4大类,主要发育玄武岩、角砾熔岩、含凝灰角砾熔岩、凝灰岩和沉凝灰岩等岩石类型;②该盆地内大面积分布溢流相、喷溢相和火山沉积相等3种火山岩相类型,其中溢流相主要发育玄武岩,喷溢相主要发育火山碎屑熔岩,火山沉积相主要发育凝灰岩及沉凝灰岩等;③火山岩储层岩性主要为火山碎屑熔岩和玄武岩,其中火山碎屑熔岩主要发育脱玻化微孔、溶蚀孔,为中孔、低渗的孔隙型储层,玄武岩主要发育裂缝及溶孔,为基质孔隙度较低的孔隙—裂缝型储层;④火山岩储层控制因素主要为岩性、岩相、后期流体改造作用和构造作用,其中火山碎屑熔岩在快速冷凝的过程中脱玻化形成大量弥散状微孔,为后期进一步溶蚀增孔提供了有利条件,溶蚀等成岩作用及裂缝发育使储层物性变好。结论认为,四川盆地二叠系火山岩储层的平面展布主要受岩相控制,川西南部雅安—乐山—屏山地区主要发育孔隙—裂缝型玄武岩储层,成都—简阳—三台地区主要发育孔隙型火山碎屑熔岩储层。

Lithofacies and reservoir characteristics of Permian volcanic rocks in the Sichuan Basin

In order to provide basis for further exploration and deployment of volcanic gas reservoirs in the Sichuan Basin, we classified Permian volcanic rocks in this basin using drilling, mud logging, assay, logging and seismic data comprehensively. Then, the lithological characteristics, lithofacies characteristics, lithofacies distribution and reservoir characteristics of different types of volcanic rocks were studied. Besides, the main factors controlling the development of volcanic reservoirs were determined. And the following research results were obtained. First, volcanic rocks in the Sichuan Basin can be comprehensively classified into 4 categories (i.e., volcanic lava, vocaniclastic lava, volcaniclastic rocks and sedimentary volcaniclastic rocks), and basalt, breccia lava, tuffaceous breccia lava, tuff, sedimentary tuff are mainly developed. Second, 3 types of volcanic lithofacies are extensively developed in the Sichuan Basin, including overflow facies, effusive facies and volcanic sedimentary facies. Overflow facies is mainly dominated by basalt, effusive facies is mainly composed of volcaniclastic lava, and volcanic sedimentary facies is mainly composed of tuff and sedimentary tuff. Third, volcanic reservoirs are lithologically composed of breccia lava and basalt. Breccia lava reservoirs are pore-type reservoirs of moderate porosity and low permeability with devitrified micropores and dissolution pores as main reservoir space. In basalt, fractures and dissolution pores are mainly developed, and they are porous-fractured reservoirs with lower matrix porosity. Fourth, the factors controlling volcanic reservoirs mainly include lithology, lithofacies, later fluid alteration and tectonism. Volcaniclastic lava is devitrified in the process of rapid condensation, and a great number of dispersion-shape micropores are formed to provide favorable conditions for further dissolution and pore enhancement in the later stage. Post-diagenesis effect (e.g. dissolution) and fracture development make the reservoir properties better. In conclusion, the areal distribution of volcanic reservoirs in the Sichuan Basin is mainly controlled by the lithofacies. Porous-fractured basalt reservoirs are mainly developed in the Ya'an–Leshan–Pingshan area in the southwestern Sichuan Basin, and pore-type vocaniclastic lava reservoirs are mainly developed in the Chengdu–Jianyang–Santai area.